The invention relates to the membrane separation of water from aqueous mixtures of organic and inorganic compounds. In another aspect the invention relates to the membrane separation of water from aqueous mixtures wherein the organic and inorganic compounds are soluble or dispersable in water. Yet in another aspect, the invention relates to the membrane separation of water from aqueous feed mixtures coupled with the use of a water miscible sweep liquid which allows for permeate water separation without change of phase. Still another aspect of the invention relates to the process wherein an aqueous mixture can be more highly concentrated by the removal of at least a portion of the water from the feed mixture.
The separation of water from aqueous mixtures such as dispersions, emulsions, solutions, and the like has been accomplished by various means, for example, distillation, filtration, solvent extraction and combinations of these and other methods. However, these methods often fail to provide satisfactory water separation from aqueous mixtures without the utilization of multiple unit apparatus or the high energy input required by phase change techniques. Known filtration methods also fail to be effective when particle size of the dispersion or emulsion is of such minuteness that the particles pass through the filter material with the water. Solvent extraction methods frequently result in the exchange of one aqueous mixture for another thus presenting the continuing need for water separation from an aqueous mixture or solution. Because of the disadvantages of the existing methods for water separation from aqueous mixtures, a simple, inexpensive process adaptable for all types of aqueous mixtures is highly desirable.
Membrane separation techniques have been utilized to separate mixtures of two or more different molecules, for example, aqueous mixtures, mixed hydrocarbons, azeotropic mixtures, and the like. However, known separation techniques utilized in the separation of aqueous mixtures, frequently are followed by secondary procedures such as distillation. Because of the disadvantages of existing separation methods which principally involve a substantial energy input of a thermal, chemical, or mechanical nature, a simple membrane separation process for separating water from aqueous mixtures involving a minimum energy input is needed.
The growing need for additional sources of water from salt water or from contaminated sources has directed intensive investigations into the separation of water from aqueous mixtures. Substantial improvements have been made in known water separation procedures based on flash evaporation, membrane separation, electrodialytic action, freezing, and the like. However, even with improvements, such known procedures require substantial amounts of power and heat differentials, and frequently require a physical phase change in the system such as vaporization or crystallization. In order to achieve an inexpensive water separation from aqueous mixtures of organic and inorganic compounds, techniques must be developed which require a minimum energy input, avoid phase change, or both.
Accordingly, an object of this invention is to provide improved procedures for separating water from aqueous mixtures wherein power and heat differential requirements are markedly reduced.
Another object of this invention is to provide improved water separation procedures which require relatively simple equipment having low power requirements and minimal thermal values.